package mirror.android.os;


//import java.util.ArrayDeque;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.Callable;
import java.util.concurrent.CancellationException;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Executor;
import java.util.concurrent.FutureTask;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicInteger;

import android.os.Handler;
import android.os.Message;
import android.os.Process;

@SuppressWarnings({ "unchecked", "rawtypes" })
public abstract class AsyncTask<Params, Progress, Result> {
  private static final String LOG_TAG = "AsyncTask";

  private static final int CORE_POOL_SIZE = 5;
  private static final int MAXIMUM_POOL_SIZE = 128;
  private static final int KEEP_ALIVE = 1;

  private static final ThreadFactory sThreadFactory = new ThreadFactory() {
      private final AtomicInteger mCount = new AtomicInteger(1);

      public Thread newThread(Runnable r) {
          return new Thread(r, "AsyncTask #" + mCount.getAndIncrement());
      }
  };

  private static final BlockingQueue<Runnable> sPoolWorkQueue =
          new LinkedBlockingQueue<Runnable>(10);

  /**
   * An {@link Executor} that can be used to execute tasks in parallel.
   */
  public static final Executor THREAD_POOL_EXECUTOR
          = new ThreadPoolExecutor(CORE_POOL_SIZE, MAXIMUM_POOL_SIZE, KEEP_ALIVE,
                  TimeUnit.SECONDS, sPoolWorkQueue, sThreadFactory);

  /**
   * An {@link Executor} that executes tasks one at a time in serial
   * order.  This serialization is global to a particular process.
   */
//  public static final Executor SERIAL_EXECUTOR = new SerialExecutor();

  private static final int MESSAGE_POST_RESULT = 0x1;
  private static final int MESSAGE_POST_PROGRESS = 0x2;

  private static final InternalHandler sHandler = new InternalHandler();

//  private static volatile Executor sDefaultExecutor = SERIAL_EXECUTOR;
  private static volatile Executor sDefaultExecutor = THREAD_POOL_EXECUTOR;
  private final WorkerRunnable<Params, Result> mWorker;
  private final FutureTask<Result> mFuture;

  private volatile Status mStatus = Status.PENDING;

  private final AtomicBoolean mTaskInvoked = new AtomicBoolean();

//  private static class SerialExecutor implements Executor {
//      final ArrayDeque<Runnable> mTasks = new ArrayDeque<Runnable>();
//      Runnable mActive;
//
//      public synchronized void execute(final Runnable r) {
//          mTasks.offer(new Runnable() {
//              public void run() {
//                  try {
//                      r.run();
//                  } finally {
//                      scheduleNext();
//                  }
//              }
//          });
//          if (mActive == null) {
//              scheduleNext();
//          }
//      }
//
//      protected synchronized void scheduleNext() {
//          if ((mActive = mTasks.poll()) != null) {
//              THREAD_POOL_EXECUTOR.execute(mActive);
//          }
//      }
//  }

  /**
   * Indicates the current status of the task. Each status will be set only once
   * during the lifetime of a task.
   */
  public enum Status {
      /**
       * Indicates that the task has not been executed yet.
       */
      PENDING,
      /**
       * Indicates that the task is running.
       */
      RUNNING,
      /**
       * Indicates that {@link AsyncTask#onPostExecute} has finished.
       */
      FINISHED,
  }

  /** @hide Used to force static handler to be created. */
  public static void init() {
      sHandler.getLooper();
  }

  /** @hide */
  public static void setDefaultExecutor(Executor exec) {
      sDefaultExecutor = exec;
  }

  /**
   * Creates a new asynchronous task. This constructor must be invoked on the UI thread.
   */
  public AsyncTask() {
      mWorker = new WorkerRunnable<Params, Result>() {
          public Result call() throws Exception {
              mTaskInvoked.set(true);

              Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);
              return postResult(doInBackground(mParams));
          }
      };

      mFuture = new FutureTask<Result>(mWorker) {
          @Override
          protected void done() {
              try {
                  final Result result = get();

                  postResultIfNotInvoked(result);
              } catch (InterruptedException e) {
                  android.util.Log.w(LOG_TAG, e);
              } catch (ExecutionException e) {
                  throw new RuntimeException("An error occured while executing doInBackground()",
                          e.getCause());
              } catch (CancellationException e) {
                  postResultIfNotInvoked(null);
              } catch (Throwable t) {
                  throw new RuntimeException("An error occured while executing "
                          + "doInBackground()", t);
              }
          }
      };
  }

  private void postResultIfNotInvoked(Result result) {
      final boolean wasTaskInvoked = mTaskInvoked.get();
      if (!wasTaskInvoked) {
          postResult(result);
      }
  }

  private Result postResult(Result result) {
	Message message = sHandler.obtainMessage(MESSAGE_POST_RESULT,
              new AsyncTaskResult<Result>(this, result));
      message.sendToTarget();
      return result;
  }

  /**
   * Returns the current status of this task.
   *
   * @return The current status.
   */
  public final Status getStatus() {
      return mStatus;
  }

  /**
   * Override this method to perform a computation on a background thread. The
   * specified parameters are the parameters passed to {@link #execute}
   * by the caller of this task.
   *
   * This method can call {@link #publishProgress} to publish updates
   * on the UI thread.
   *
   * @param params The parameters of the task.
   *
   * @return A result, defined by the subclass of this task.
   *
   * @see #onPreExecute()
   * @see #onPostExecute
   * @see #publishProgress
   */
  protected abstract Result doInBackground(Params... params);

  /**
   * Runs on the UI thread before {@link #doInBackground}.
   *
   * @see #onPostExecute
   * @see #doInBackground
   */
  protected void onPreExecute() {
  }

  /**
   * <p>Runs on the UI thread after {@link #doInBackground}. The
   * specified result is the value returned by {@link #doInBackground}.</p>
   * 
   * <p>This method won't be invoked if the task was cancelled.</p>
   *
   * @param result The result of the operation computed by {@link #doInBackground}.
   *
   * @see #onPreExecute
   * @see #doInBackground
   * @see #onCancelled(Object) 
   */
  protected void onPostExecute(Result result) {
  }

  /**
   * Runs on the UI thread after {@link #publishProgress} is invoked.
   * The specified values are the values passed to {@link #publishProgress}.
   *
   * @param values The values indicating progress.
   *
   * @see #publishProgress
   * @see #doInBackground
   */
  protected void onProgressUpdate(Progress... values) {
  }

  /**
   * <p>Runs on the UI thread after {@link #cancel(boolean)} is invoked and
   * {@link #doInBackground(Object[])} has finished.</p>
   * 
   * <p>The default implementation simply invokes {@link #onCancelled()} and
   * ignores the result. If you write your own implementation, do not call
   * <code>super.onCancelled(result)</code>.</p>
   *
   * @param result The result, if any, computed in
   *               {@link #doInBackground(Object[])}, can be null
   * 
   * @see #cancel(boolean)
   * @see #isCancelled()
   */
  protected void onCancelled(Result result) {
      onCancelled();
  }    

  /**
   * <p>Applications should preferably override {@link #onCancelled(Object)}.
   * This method is invoked by the default implementation of
   * {@link #onCancelled(Object)}.</p>
   * 
   * <p>Runs on the UI thread after {@link #cancel(boolean)} is invoked and
   * {@link #doInBackground(Object[])} has finished.</p>
   *
   * @see #onCancelled(Object) 
   * @see #cancel(boolean)
   * @see #isCancelled()
   */
  protected void onCancelled() {
  }

  /**
   * Returns <tt>true</tt> if this task was cancelled before it completed
   * normally. If you are calling {@link #cancel(boolean)} on the task,
   * the value returned by this method should be checked periodically from
   * {@link #doInBackground(Object[])} to end the task as soon as possible.
   *
   * @return <tt>true</tt> if task was cancelled before it completed
   *
   * @see #cancel(boolean)
   */
  public final boolean isCancelled() {
      return mFuture.isCancelled();
  }

  /**
   * <p>Attempts to cancel execution of this task.  This attempt will
   * fail if the task has already completed, already been cancelled,
   * or could not be cancelled for some other reason. If successful,
   * and this task has not started when <tt>cancel</tt> is called,
   * this task should never run. If the task has already started,
   * then the <tt>mayInterruptIfRunning</tt> parameter determines
   * whether the thread executing this task should be interrupted in
   * an attempt to stop the task.</p>
   * 
   * <p>Calling this method will result in {@link #onCancelled(Object)} being
   * invoked on the UI thread after {@link #doInBackground(Object[])}
   * returns. Calling this method guarantees that {@link #onPostExecute(Object)}
   * is never invoked. After invoking this method, you should check the
   * value returned by {@link #isCancelled()} periodically from
   * {@link #doInBackground(Object[])} to finish the task as early as
   * possible.</p>
   *
   * @param mayInterruptIfRunning <tt>true</tt> if the thread executing this
   *        task should be interrupted; otherwise, in-progress tasks are allowed
   *        to complete.
   *
   * @return <tt>false</tt> if the task could not be cancelled,
   *         typically because it has already completed normally;
   *         <tt>true</tt> otherwise
   *
   * @see #isCancelled()
   * @see #onCancelled(Object)
   */
  public final boolean cancel(boolean mayInterruptIfRunning) {
      return mFuture.cancel(mayInterruptIfRunning);
  }

  /**
   * Waits if necessary for the computation to complete, and then
   * retrieves its result.
   *
   * @return The computed result.
   *
   * @throws CancellationException If the computation was cancelled.
   * @throws ExecutionException If the computation threw an exception.
   * @throws InterruptedException If the current thread was interrupted
   *         while waiting.
   */
  public final Result get() throws InterruptedException, ExecutionException {
      return mFuture.get();
  }

  /**
   * Waits if necessary for at most the given time for the computation
   * to complete, and then retrieves its result.
   *
   * @param timeout Time to wait before cancelling the operation.
   * @param unit The time unit for the timeout.
   *
   * @return The computed result.
   *
   * @throws CancellationException If the computation was cancelled.
   * @throws ExecutionException If the computation threw an exception.
   * @throws InterruptedException If the current thread was interrupted
   *         while waiting.
   * @throws TimeoutException If the wait timed out.
   */
  public final Result get(long timeout, TimeUnit unit) throws InterruptedException,
          ExecutionException, TimeoutException {
      return mFuture.get(timeout, unit);
  }

  /**
   * Executes the task with the specified parameters. The task returns
   * itself (this) so that the caller can keep a reference to it.
   * 
   * <p>Note: this function schedules the task on a queue for a single background
   * thread or pool of threads depending on the platform version.  When first
   * introduced, AsyncTasks were executed serially on a single background thread.
   * Starting with {@link android.os.Build.VERSION_CODES#DONUT}, this was changed
   * to a pool of threads allowing multiple tasks to operate in parallel.  After
   * {@link android.os.Build.VERSION_CODES#HONEYCOMB}, it is planned to change this
   * back to a single thread to avoid common application errors caused
   * by parallel execution.  If you truly want parallel execution, you can use
   * the {@link #executeOnExecutor} version of this method
   * with {@link #THREAD_POOL_EXECUTOR}; however, see commentary there for warnings on
   * its use.
   *
   * <p>This method must be invoked on the UI thread.
   *
   * @param params The parameters of the task.
   *
   * @return This instance of AsyncTask.
   *
   * @throws IllegalStateException If {@link #getStatus()} returns either
   *         {@link AsyncTask.Status#RUNNING} or {@link AsyncTask.Status#FINISHED}.
   */
  public final AsyncTask<Params, Progress, Result> execute(Params... params) {
      return executeOnExecutor(sDefaultExecutor, params);
  }

  /**
   * Executes the task with the specified parameters. The task returns
   * itself (this) so that the caller can keep a reference to it.
   * 
   * <p>This method is typically used with {@link #THREAD_POOL_EXECUTOR} to
   * allow multiple tasks to run in parallel on a pool of threads managed by
   * AsyncTask, however you can also use your own {@link Executor} for custom
   * behavior.
   * 
   * <p><em>Warning:</em> Allowing multiple tasks to run in parallel from
   * a thread pool is generally <em>not</em> what one wants, because the order
   * of their operation is not defined.  For example, if these tasks are used
   * to modify any state in common (such as writing a file due to a button click),
   * there are no guarantees on the order of the modifications.
   * Without careful work it is possible in rare cases for the newer version
   * of the data to be over-written by an older one, leading to obscure data
   * loss and stability issues.  Such changes are best
   * executed in serial; to guarantee such work is serialized regardless of
   * platform version you can use this function with {@link #SERIAL_EXECUTOR}.
   *
   * <p>This method must be invoked on the UI thread.
   *
   * @param exec The executor to use.  {@link #THREAD_POOL_EXECUTOR} is available as a
   *              convenient process-wide thread pool for tasks that are loosely coupled.
   * @param params The parameters of the task.
   *
   * @return This instance of AsyncTask.
   *
   * @throws IllegalStateException If {@link #getStatus()} returns either
   *         {@link AsyncTask.Status#RUNNING} or {@link AsyncTask.Status#FINISHED}.
   */
  public final AsyncTask<Params, Progress, Result> executeOnExecutor(Executor exec,
          Params... params) {
      if (mStatus != Status.PENDING) {
          switch (mStatus) {
              case RUNNING:
                  throw new IllegalStateException("Cannot execute task:"
                          + " the task is already running.");
              case FINISHED:
                  throw new IllegalStateException("Cannot execute task:"
                          + " the task has already been executed "
                          + "(a task can be executed only once)");
		default:
			break;
          }
      }

      mStatus = Status.RUNNING;

      onPreExecute();

      mWorker.mParams = params;
      exec.execute(mFuture);

      return this;
  }

  /**
   * Convenience version of {@link #execute(Object...)} for use with
   * a simple Runnable object.
   */
  public static void execute(Runnable runnable) {
      sDefaultExecutor.execute(runnable);
  }

  /**
   * This method can be invoked from {@link #doInBackground} to
   * publish updates on the UI thread while the background computation is
   * still running. Each call to this method will trigger the execution of
   * {@link #onProgressUpdate} on the UI thread.
   *
   * {@link #onProgressUpdate} will note be called if the task has been
   * canceled.
   *
   * @param values The progress values to update the UI with.
   *
   * @see #onProgressUpdate
   * @see #doInBackground
   */
  protected final void publishProgress(Progress... values) {
      if (!isCancelled()) {
          sHandler.obtainMessage(MESSAGE_POST_PROGRESS,
                  new AsyncTaskResult<Progress>(this, values)).sendToTarget();
      }
  }

  private void finish(Result result) {
      if (isCancelled()) {
          onCancelled(result);
      } else {
          onPostExecute(result);
      }
      mStatus = Status.FINISHED;
  }

  private static class InternalHandler extends Handler {
	@Override
      public void handleMessage(Message msg) {
          AsyncTaskResult result = (AsyncTaskResult) msg.obj;
          switch (msg.what) {
              case MESSAGE_POST_RESULT:
                  // There is only one result
                  result.mTask.finish(result.mData[0]);
                  break;
              case MESSAGE_POST_PROGRESS:
                  result.mTask.onProgressUpdate(result.mData);
                  break;
          }
      }
  }

  private static abstract class WorkerRunnable<Params, Result> implements Callable<Result> {
      Params[] mParams;
  }

  private static class AsyncTaskResult<Data> {
	final AsyncTask mTask;
      final Data[] mData;

	AsyncTaskResult(AsyncTask task, Data... data) {
          mTask = task;
          mData = data;
      }
  }
}